A labor for removing axillary buds just before harvesting of tobacco is necessary for securing the yield and quality of leaf tobacco. However, in order to perform the labor by hand work, a huge amount of work is required. Therefore, nowadays, a method involving spraying an inhibitor for tobacco axillary bud growth has been developed and widely used.
As an inhibitor for tobacco axillary bud growth which has been widely used from the Showa 30's (1955-1964), there is known inhibitors including, as an active ingredient, maleic hydrazide or a salt thereof, having a systemic action. The inhibitor is actually used at a concentration as high as about 5,000 ppm and is poor in terms of sustained chemical efficacy. Hence, there has been a problem in that a large amount of the inhibitor is required. Further, hydrazine produced by decomposition of maleic hydrazide exhibits oncogenic potential, and hence use of the inhibitor is currently restricted.
Therefore, in recent years, a contact-type inhibitor for tobacco axillary bud growth, which is sprayed by contact with stem, has been used. As the contact-type inhibitor, there are known, for example, an inhibitor including a saturated aliphatic alcohol as an active ingredient and an inhibitor including a dinitroaniline-based chemical substance as an active ingredient.
The inhibitor for axillary bud growth including a saturated aliphatic alcohol as an active ingredient has a high effect of killing axillary buds by contact. However, the inhibitor including a saturated aliphatic alcohol as an active ingredient is poor in terms of sustained chemical efficacy and requires spraying of the inhibitor at least twice in order to prevent elongation of axillary buds in the later growth period. In addition, attachment of the sprayed inhibitor to leaves at the time of use causes bleaching, another harmful effect of the inhibitor, and reduction in quality of the leaves. Further, as the inhibitor is dropped and accumulated at the base part of a plant, all stem bases are necrotized, resulting in killing the plant.
On the other hand, the inhibitor including a dinitroaniline-based chemical substance as an active ingredient is disclosed in, for example, U.S. Pat. No. 3,672,866 A (Patent Document 1), U.S. Pat. No. 4,046,809 A (Patent Document 2) and U.S. Pat. No. 4,123,250 A (Patent Document 3). The inhibitor including a dinitroaniline-based compound as an active ingredient contains a certain organic solvent. The inhibitor has an effect of stopping growth of axillary buds by dehydrating and necrotizing axillary buds by contact of the dinitroaniline-based chemical substance and the organic solvent with the axillary buds and allowing the above-mentioned chemical substance to be absorbed from the axillary bud plumule part or from wounds after removal of the axillary buds to inhibit cell division and has a high effect of inhibiting formation and elongation of axillary buds.
However, the inhibitor including a dinitroaniline-based chemical substance as an active ingredient has the following problems, for example. The inhibitor sometimes causes harmful effects such as deformation of young leaves of the upper node, lack in expansion, necrosis of mesophyll, damages of the petiole parts of middle or upper leaves, developmental disorders of adventitious roots, and necrosis immediately after spraying; and induces diseases such as hollow heart, crown rot, and gray mold from wound sites formed in the petiole base by the harmful effects to cause adverse effects on the yield and quality of leaf tobacco.
As mentioned above, the inhibitor for axillary bud growth currently used in cultivation of tobacco have many problems yet to be solved from the viewpoint of sustainment of the chemical efficacy and occurrence of harmful effects.
Therefore, an inhibitor for tobacco axillary bud growth which is excellent in terms of sustained chemical efficacy, induces no harmful effect and no disease, and can contribute to improvement in labor productivity has been desired.
A cell division inhibitor of a pyridine-based compound or a benzamide-based compound to be used in the present invention is a known compound, and for example, JP 04-47667 B (Patent Document 4, U.S. Pat. No. 4,692,184), JP 06-60171 B (Patent Document 5, U.S. Pat. No. 4,988,384), U.S. Pat. No. 3,640,699 (Patent Document 6), JP 53-43569 B (Patent Document 7, U.S. Pat. No. 3,707,366) describe that dithiopyr, thiazopyr, propyzamide or tebutam are used as herbicides, respectively. Hitherto, however, the cell division inhibitor of a pyridine-based compound or a benzamide-based compound has not been used as an inhibitor for tobacco axillary bud growth.
In the present invention, the cell division inhibitor means a drug inhibiting cell proliferation by ceasing mitotic division of plant cells.